Mandatory Browser Extensions For All Web Developers

Ok, two blogs in a row—both courtesy of Rob.
I was browsing through his archieves and found
an entry about a cool
extension for Firefox/Mozilla that does all sorts
of really cool stuff for Web Developers. I can
think of a number of times when a tool like this
would have been useful in the past. Unfortunately,
there's been an IE tool that's similiar that I never
knew about. Geez! Anyway, check out the following
tools that should be useful to any web developer.